1. Field of the Invention
This invention relates to an electrophotographic endless belt, such as a transfer material transporting belt, an intermediate transfer belt or a photosensitive belt, used in an electrophotographic apparatus, and also relates to an electrophotographic apparatus having the electrophotographic endless belt, and a process for producing the electrophotographic endless belt.
2. Related Background Art
Besides rigid-body drum-shaped members, flexible endless-belt-shaped members (electrophotographic endless belts) are conventionally used in transfer material transporting members, intermediate transfer members, electrophotographic photosensitive members, fixing members and so forth used in electrophotographic apparatuses, such as copying machines and laser beam printers.
In recent years, color (such as full-color) electrophotographic apparatuses have been put forward into practical use, and there is an increasing demand for transfer material transporting belts, intermediate transfer belts and so forth as well.
An endless belt composed chiefly of a thermoplastic resin is commonly available as the electrophotographic endless belt. The endless belt composed chiefly of a thermoplastic resin has advantages in that it can be produced at a low cost and general-purpose extruding machines can be used.
For example, Japanese Patent Application Laid-open No. H03-089357 discloses an electrophotographic endless belt making use of a polycarbonate, which is a thermoplastic resin. However, the polycarbonate resin disclosed in Japanese Patent Application Laid-open No. H03-089357 is a non-crystalline resin. Hence, the electrophotographic endless belt making use of it has poor flexing resistance.
For example, Japanese Patent Application Laid-open No. H08-099374 discloses an electrophotographic endless belt making use of polyalkylene terephthalate, which is a crystalline resin, in order to improve flexing resistance. The use of such a crystalline resin may lead to superior flexing resistance. However, where carbon black is used therein as a conducting agent, the resin may become too brittle, resulting in an electrophotographic endless belt having poor flexing resistance even though the resin itself has good flexing resistance.
Thus, in using carbon black as a conducting agent, it is necessary for the resin to have flexing resistance and also be more flexible.
Japanese Patent Application Laid-open No. H05-016263 discloses an electrophotographic endless belt making use of a polyamide resin, which is a flexible, crystalline resin. However, polyamide 6 or polyamide 66, which is a commonly available polyamide resin, has a high concentration of amide groups. Hence, the use of polyamide 6 or polyamide 66 may lead to high water absorption, causing dimensional changes or greatly varying the electrical properties due to the service environment. Thus, it has been difficult to use such a resin.
Accordingly, it may be contemplated to use, among polyamide resins, a polyamide having an especially low water absorption. However, the polyamide having a low water absorption may inevitably also have a low modulus of elasticity at the same time. When it is used alone, the resultant electrophotographic endless belt may creep (elongate) and not be durable enough for long-term service.
Japanese Patent Application Laid-open No. 2001-350347 discloses an electrophotographic endless belt making use of polyamide resin 12, having a low water absorption, and carbon black. In fact, the incorporation of carbon black as a conducting agent improves the modulus of elasticity by the virtue of its reinforcing effect, and may reduce creeping. However, its effect is not sufficient depending on the types of carbon black, and the belt has not been sufficiently durable for long-term service.
Thus, the mere use of a polyamide resin and carbon black has not been unable to provide an electrophotographic endless belt that has satisfactory creep resistance.
Japanese Patent Application Laid-open No. 2003-177612 discloses an electrophotographic endless belt making use of a polyamide resin and carbon black to which an inorganic filler has been added. In the electrophotographic endless belt disclosed in Japanese Patent Application Laid-open No. 003-177612, barium sulfate is used as the inorganic filler.
However, when barium sulfate is used as the inorganic filler, it may have an effect on dispersibility, as disclosed in Japanese Patent Application Laid-open No. 2003-177612, and is insufficient to provide a reinforcing effect, consequently causing creeping to occur. In order to improve the reinforcing effect, a large quantity of barium sulfate must be added. However, although the addition of such a large quantity of barium sulfate may reduce creeping, it may make the belt highly brittle, so that breaking or chipping occurs when the electrophotographic endless belt is repeatedly flexed.
Now, usually, it is common for the electrical resistance of the electrophotographic endless belt to be controlled by dispersing a conducting agent in a binder resin. For example, a method is available in which an organic antistatic agent or an electrolyte is dispersed in a binder resin. In this method, a surface-active agent or a hydrophilic resin is commonly used as the organic antistatic agent, and a metal salt, such as a lithium salt or a potassium salt, is commonly used as the electrolyte.
However, in the case when the surface-active agent or metal salt is used, while surface resistivity may decrease, it may be difficult to decrease volume resistivity. To control the volume resistivity, a large quantity of the surface-active agent or metal salt must be added, which brings about a problem of this additive leaching out to the surface of the electrophotographic endless belt.
In the case when the hydrophilic resin is used, the electrical resistance cannot be decreased unless a fairly large quantity of it is added to the binder resin. Hence, the electrical resistance of the belt may depend to a large extent on the environmental conditions, which is not desirable.
In addition, where a large quantity of a metal salt having deliquescent properties, such as the lithium salt, is dispersed in the binder resin, there has been a difficulty in that the electrical resistance is greatly affected by moisture.